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SubjectRe: [PATCH 4/5] perf/hw_breakpoint: Set breakpoint as disabled in modify_user_hw_breakpoint error path
On 08/09, Jiri Olsa wrote:
>
> @@ -523,8 +523,10 @@ int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *att
> perf_event_disable(bp);
>
> err = modify_user_hw_breakpoint_check(bp, attr, false);
> - if (err)
> + if (err) {
> + bp->attr.disabled = 1;
> return err;

Yes, but on the second thought... Can't we simply do

int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
{
int err;

/*
* modify_user_hw_breakpoint can be invoked with IRQs disabled and hence it
* will not be possible to raise IPIs that invoke __perf_event_disable.
* So call the function directly after making sure we are targeting the
* current task.
*/
if (irqs_disabled() && bp->ctx && bp->ctx->task == current)
perf_event_disable_local(bp);
else
perf_event_disable(bp);

err = modify_user_hw_breakpoint_check(bp, attr, false);

if (!bp.attr->disabled)
perf_event_enable(bp);

return err;
}

instead of this and the next patch?

We can do this because (as you pointed out) validate_hw_breakpoint() has already
gone in -tip tree, and (afaics) modify_user_hw_breakpoint_check() never changes
perf_event's state on failure, so we can safely "restart" this bp if it was enabled
before.

1. This is what we had before the recent f67b15037a7a50c57f72e69a6d59941ad90a0f0f
"perf/hwbp: Simplify the perf-hwbp code, fix documentation".

Note that this commit was actually the bug fix which introduced another problem
fixed by your 2/5.

But see above, perf_event_enable() is no longer unsafe after
modify_user_hw_breakpoint_check(), we can restore the previous semantics.

2. This matches perf_event_modify_breakpoint(). Which btw can be simplified a bit,
it too can simply do

if (!bp->attr.disabled)
_perf_event_enable(bp);

return err;

Oleg.

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